Commercial electricity is produced by steam-driven turbines. The steam is produced from burning fossil fuels or through nuclear fusion reactors or by building dams across rivers to drive hydro turbines. All of these power-generating activities, come with a heavy environmental toll and with massive climate changing consequences. One better way to generate clean electrical power is from the perpetual undulatory motions of oceanic water waves. Oceanic water waves are virtually an inexhaustible source of clean energy. Numerous devices that convert water wave energy into electrical power have been described in the prior art. However, only a limited number of these devices have been put into practice under real conditions. A review of prior art water wave energy devices shows that many of the prior art water wave energy devices (E.g., U.S. Pat. Nos. 4,443,708 and 9,018,779 are not capable of storing extracted water wave energy, but only convey unstored extracted water wave energy into a power grid on land. However, because of random variability in sea state conditions, the amount of water wave energy that may be transmitted to a land-based power grid varies significantly during any year and cannot be predicted or controlled. At the same time, a demand on energy at a land-based power grid is also highly randomly variable. For instance, it is possible that peak electrical energy production from water wave kinetic energy devices may occur at times of low electrical energy demand for land-based power grids. High demand for energy during the summer months may coincide with the low tide season and smaller tidal wave availability at sea. Conversely, low demand on land-based power grids may coincide with higher energy production due to higher tidal water wave frequency at sea. Thus, it is likely that peak energy demand at land-based power grids may not coincide with peak energy production by prior art water wave energy devices. Another limitation of certain prior art devices is that, because of an incapability to store the produced energy, the efficiency of some prior art water wave energy devices may be relatively low. In addition, storing energy on site at sea may be advantageous for oceanic shipping lanes wherefrom ships may refuel on high seas without having to make an end-run for energy refueling to the nearest port of call or other land-based energy sources, thus facilitating at sea refueling and obviating the need for a port call.
U.S. Pat. No. 8,193,651 issued to Lightfoot, et al., discloses a method of storage of extracted water wave energy in the form of hydrogen. This method includes extraction of ocean water wave energy at or near shore area and applies the energy to electrolyze ocean water to produce hydrogen gas from ocean water. The hydrogen gas is further pumped onshore for land-based storage. The disadvantage of such a storage method is that the water wave energy converter, generator, and electrolyzer are located at a near shore area (at the area of water wave impact), while storage for hydrogen gas is located on land. Thus, in order to store the extracted water wave energy, the hydrogen produced by an electrolyzer needs to be transported on land through a system of pipelines across the near shore area.
Prior art teaches that near shore areas are subject to impact by breaking water waves. Larger and more frequent water waves result in more violent conditions of breaking water waves at near shore area with consequential damages to shoreline and all facilities, including electrical facilities at near shore areas. Since the method in U.S. Pat. No. 8,193,651 relies on large water waves at near shore zone to produce water wave energy, violent breaking water wave conditions may be expected to disrupt installations as disclosed in prior art U.S. Pat. No. 8,193,651, including converter and hydrogen pipelines at these near shore areas. Significant capital investment and frequent maintenance work would then be required to maintain prior art systems of pipelines in operable condition. The advantage of the instant disclosure is that all constituents of the disclosed system, including energy converter, energy generator, water electrolyzer, compressor, storage facilities etc., are installed on a single off-shore floating platform base.
The prior art water wave energy devices (U.S. Pat. Nos. 4,443,708, 8,193,651, and 9,018,779) were developed to transmit extracted water wave energy into a power grid that is located on land via connecting power lines. Therefore, the prior art devices need to be located in close proximity to the land on near shore areas.
The following problems are associated with near shore land-based power grid installations tethered to offshore water wave energy extraction systems. Any commercial installation at a near shore coastal area would be subject to environmental legislative regulations which include complicated and lengthy permits and licenses. If permitted, the commercial installation would also require disaster mitigation measures that would significantly increase installation and maintenance costs.
Most prior art water wave energy devices are based on one of two concepts for extracting energy from water waves: (1) floating device or parts thereof on water waves: E.g., U.S. Pat. Nos. 5,066,867, 7,245,041, 7,319,278, US PG PUB. Nos. 20120096847, 20110121572, 20090115192; or (2) moving water waves through a device or parts thereof: E.g., U.S. Pat. Nos. 3,783,302; 4,260,901, 4,443,708; 4,622,471. Due to salt water-induced corrosion, clogging by oceanic flora and fauna, and floating debris, the water wave energy devices of either of these two types are subject to extensive wear and tear and malfunction. This wear and tear diminishes the efficient functioning of prior art device by reducing efficiency of energy production and requiring extensive maintenance work, thus increasing the overall cost of energy production.
Some prior art devices may provide efficient extraction of water wave energy only at certain sea state conditions characterized by water wave height, water wave frequencies, water wave length and water wave periodicity. For example, the device in U.S. Pat. No. 9,018,779 was adapted to suit a specific site with a specific water wavelength expected at that specific site. Furthermore, the length of individual members of this device is determined by the expected water wavelength at a specific site. This means that when water wave lengths differ from water wave lengths specified in the prior art device location site, the device may perform at suboptimal levels for extracting energy from water waves or the prior art device does not perform at all. It is common knowledge that sea state conditions randomly vary over time. Thus, there is a high probability that the prior art device may not perform at acceptable levels when power demands are high. For example, two prior art devices are discussed below: (1) U.S. Pat. No. 8,193,651: Method and Apparatus for Ocean Energy Conversion, Storage and Transportation to Shore; and (2) U.S. Pat. No. 8,973,359: Floating Wave Powered generator.
(1) U.S. Pat. No. 8,193,651: Method and Apparatus for Ocean Energy Conversion, Storage, and Transportation to Shore. The apparatus is comprised of a fleet of vessels attached together in longitudinal and transversal directions by special attachment mechanisms. These attachment mechanisms allow roll, pitch, and heave movements of each element (individual vessel) of the fleet. The attachment mechanism includes a hydraulic cylinder located midway between the attached vessels in a way that any relative movement between the individual vessels will extend or retract the piston in the hydraulic cylinder, which will result in pressurized flow of the working fluid from which energy can be harvested. The fleet of vessels, once attached together and affected by water waves, converts water wave energy to electrical energy, which is stored in chemical form, one of which is liquified hydrogen that is stored in special tanks. When detached from the fleet, the vessels provide transportation of chemical product (from storage of energy) to coastal waterway or by navigable waterway ports of call for distribution to market centers. To effectively perform (i.e., extract water wave energy) for a wide range of sea state conditions, the system may be adjusted by altering the composition of the fleet (number and type of vessels in assembly, direction of assembly, and ballasting the vessels). There are at least two possible issues with this prototype that reduces performance efficiency and/or limits its application:
Prior art problem 1: Irregularity of ocean water waves. Ocean water waves are an irregular system of water waves of different heights, periods, and directions. Due to this irregularity, it is likely that adjacent vessels in the assembly are moving at different amplitude and phasing, resulting in inefficiency of the invented hydraulic system to extract water wave energy.
Prior art problem 2: Forces in mooring lines and anchoring system. Kinetic energy of the movable assembly (fleet) generates significant forces in the mooring lines and anchors. In order to hold such a fleet of vessels in assembly, the mooring lines must be long and heavy. As result, the motions of moored vessels in the assembly may be absorbed and modified by the mooring lines. The restricting and controlling forces of the mooring line may generate a domino effect for motions of other vessels in the assembly and dampen the natural ebb and flow of water waves, resulting in inefficiency of extracting water wave energy, as well as enormous forces on connecting devices.
(2) U.S. Pat. No. 8,973,359: The Floating Wave Powered Generator. This device includes a floating vessel with onboard pendulum mechanism, mounted on the lever arm above a platform deck of the vessel, and a power-generating mechanism driven by a gear mechanism. Because of the undulating water waves, the pendulum, being mounted on the lever arm, sways laterally around an axis of the upstanding post, causing the upstanding post to rotate, hence delivering the momentum of the pendulum to drive the power-generating mechanism via a transmission shaft and the gear mechanism. There are at least two issues with this device. In addition, the same issues discussed above for U.S. Pat. No. 8,193,651 may apply to the floating device in U.S. Pat. No. 8,973,359, which may reduce performance efficiency and limit its application: The two issues that are more specific to the device in U.S. Pat. No. 8,973,359 are as follows:
Prior art problem related to the stability of the ship Issue 1: Lateral motions of pendulum exacerbate rolling movements of the vessel, which may endanger safety conditions of vessel. To avoid risk of safety of the vessel this device would be able to perform only during mild sea state conditions; thus, application of the device is quite limited.
Prior art problem related to the variability of sea state conditions Issue 2: Amplitude and frequency of pendulum motion is a function of frequency and amplitude of vessel motion, which in turn is a function of sea state conditions (direction, period, and height of ocean water waves). There is apparently a certain narrow band width of the sea state parameters that activate motions of pendulum and, if activated, provides frequency and amplitude corresponding to optimal performance of the device. However, because of a wide spectrum of sea state conditions, it is likely the device may be working inefficiently (or may function at all) for a significant period of time.
Another example of a limited ability to extract wave energy by prior art devices is the device in non-patent publication “The SEAREV wave energy converter” (Publication of the 6th European Wave and Tidal Energy Conference Glasgow, UK, Aug. 29-Sep. 2, 2005). SEAREV is a floating device uses a cylinder that behaves mechanically like a pendulum. The rotational motion of this pendulum wheel relative to the floating hull of the device activates an electric generator. The study referenced above shows that SEAREV optimally performs only in a relatively narrow bandwidth of water wave period, between 3 to 8 seconds. However, considering that ocean water wave periods vary in a range between 3 to 20 seconds and wider, it is likely that SEAREV, if installed in the ocean would not perform optimally during a significant period of time. Hence there is wide range of unabsorbed wave energy in the wider scale of the periods 8-20 seconds.
Thus, given the limitations of prior art devices, there is need for a new type of device that can potentially surmount the above prior art limitations and problems associated to prior art devices.